A Mouse Like a House? A Pocket Elephant?



A Mouse Like a House? A Pocket Elephant?
News for Schools from the Smithsonian Institution, Office of Elementary and Secondary Education, Washington, D.C. 20560
Winter 1987
A Mouse Like a House?
Pocket Elephant?
How Size Shapes Animals, and
What the Limits Are
King Kong reaching into a high window of the Empire
State Building ... a family small enough to live in
a matchbox, cooking meals on a thimble stove outside,
chopping down dandelions with axes made from broken Christmas tree ornaments . . . a swarm of flies
as big as blimps terrorizing a city. . . ; Stories about
familiar creatures grown huge or shrunk almost to the
vanishing point have long fascinated readers and moviegoers. But could such creatures exist in real life?
What real limits are there on animals' bigness and
smallness? What effects does an animal's size have
on the animal itself?
This issue of ART TO ZOO explores these questions. Size is a theme that cuts through the incredible
ci'~"'J?l:tjJijl of biological forms. E*ploring-this. tneme
can give your students a glimpse of basic patterns that
help make sense of that diversity. Size provides examples of math operating in nature. And size is a
subject of interest to children, who have to cope every
day with being small and growing.
Large animals differ from small ones in various
intriguing ways. One particularly interesting set of
differences involves the decrease in metabolic rate that
occurs as mammals increase in size-so that small
mammals seem to live more intensely and rapidly than
large ones do. The Lesson Plan in this issue of ART
TO ZOO describes in detail one way you might approach the subject of animal size in relation to metabolic rate. The accompanying Pull-Out Page poster
and the sidebar, "Animal Sizes and Size Limits" (on
page 3), provide less detailed information about other
size-related differences among animals.
In contrast, the elephant, heavy and big"boned, is
seldom in a rush. It puts its thick legs down delib. erately, and its usual pace is unhurried. It munches
its food steadily ... breathes slowly ... and takes
time to rest. Its heart beats at halfthe speed of a human
being's, and it draws a third as many breaths per
minute. It doesn't have babies until it is in its early
teens, and the baby grows for almost two years inside
the mother before it is born. An elephant may live as
long as 60 years.
Shrews, the smallest of all mammals, move rapidly
through their lives. (Ernest P. Walker, Mammals of the
World, 3d ed., Johns Hopkins University Press, 1975)
Shrews* and Elephants
In many ways, the contrast between a shrew-sized
mammal and an elephant-sized mammal is like the
contrast between the Keystone cops and a modem
movie. The smaller animal scurries around with the
speeded-up motions of an actor in an early screen
comedy, while the larger animal proceeds at a pace
that is steady and slow.
The life of a shrew is go, go, go. With its slender
bones, a full-grown shrew can weigh as little as a
penny (though most are somewhat heavier), and it
must always be on the move. Its metabolic rate is so
high that it has to spend a lot of its time eating to stay
alive. Its heart may beat up to 20 times a second as
it scurries around after food. The smallest shrews eat
approximately their own body weight of food every
24 hours. Each day, a shrew may alternate many periods
of activity (up to 24, depending on the kind of shrew)
with periods of rest-because if it slept through the
night, it would starve to death. (In fact, a small shrew
could starve to death if it went six hours without
eating.) A shrew can have babies when it is only two
months old, and the babies develop inside the mother
for only three weeks before they are born. It seems
that for the tiny shrew, time itself has speeded up: the
events of its existence follow each other in rapid
succession, and its whole life is over in a year.
*For simplicity's sake throughout this issue, distinctions between
different kinds of the same animal are almost never made. There
are many kinds of shrews, for example, ranging in adult weight
from 2 grams to about 35 grams.
To begin to understand why shrews and elephants
differ in these ways, it is important to understand what.
metabolism is. Here is a basic explanation.
An animal breaks down into simple chemicals the
food it has digested. In this way, it releasest energy
(to heat its body and fuel its activities) and produces
matter (to build the giant molecules that it needs to
construct and repair its body).
The hundreds of chemical reactions involved in this
breaking down and building up, which take place in
the animal's cells, are together called metabolism. It
is essential that metabolism take place, because the
animal must have this energy and these body-building
materials in order to survive and reproduce.
For metabolism to happen, conditions in the cells
must be just right. For one thing, there must be enough
oxygen and water, and the temperature must be suitable. For another, there must be a means to carry away
the waste products (like carbon dioxide) that metabolism releases, so they don't poison the animal.
The speed at which these chemical processes take
place is called the metabolic rate. One way to determine an animal's metabolic rate is by measuring how
much oxygen the creature uses. The more oxygen, the
higher the metabolic rate-and the more active the
animal. Different species have different metabolic rates,
and the same animal's metabolic rate will vary depending on such factors as its activity level, the amount
of food it has eaten, and its temperature.
Body Temperature
Any animal, to survive, must find some way to keep
its body within the temperature range that allows metabolism to take place. Warm-blooded animals solve
this problem differently than cold-blooded animals do.
Although the Lesson Plan is specifically about mammals, which are warm-blooded§ the supplementary
poster includes information about cold-blooded animals as well. For this reason, background about both
groups is provided here, so you will have the information you need to give your students whatever explanations and answers they require.
• Cold-blooded animals. All animals except mammals and birds are cold-blooded, a term that is misleading, since the blood ofthese creatures is not always
cold, but varies with the temperature of their surroundings. Cold-blooded animals depend on their environment to regulate their body temperatures. When
a cold-blooded animal is too hot, it may move into
the shade. On a chilly day, it may warm up by basking
in the sun. If it is still too cold, it will become increasingly sluggish. Its metabolism slows down, so it
produces and requires less energy-which is why coldblooded animals become inactive in cold weather.
• Warm-blooded animals. Warm-blooded animals,
on the other hand, have body mechanisms that allow
them to regulate their internal temperatures to be more
or less constant no matter what the temperature of
their surroundings. Thus they can cool themselves in
hot weather (by sweating, for example, or by increasing the blood flow just under their skin so they lose
continued on page 4
Elephants, like the one shown
here with keeper Jim Jones at the
Smithsonian's National Zoological
Park, seem to take their time at
almost everything they do. (Jessie
Cohen, National Zoological Park)
A chinchilla can weigh up to 800 grams. It looks heavier than it is because of its thick fur. (Jessie Cohen,
National Zoological Park)
Lesson Plan
Step 1: Introducing Size Differences and
Ask your students what the biggest animal they can
think of is. Then, what is the smallest?
This will lead to the question, what counts as an
animal? Is a germ an animal? Tell the class that we'll
say that animals are living beings that use food from
their surroundings to produce the energy they need
to stay alive at least long enough to reproduce. (Bacteria are animals. Viruses are not, because they are
unable to reproduce without the help of a different
species of animal.)
Now have the class look at the size scale on the
Pull-Out Page. Point out that this chart goes from the
smallest animal known, Mycoplasma, which is smaller
than a bacterium but larger than a virus, all the way
up to the great blue whale, the world's largest animal.
Point out too that all the animals on the poster (and
all the animals that the children will be learning about
in this lesson) are grown-up animals.
Tell the children that they will have a chance later
on to examine the poster more carefully, and to read
about the smallest and largest animals. But first, they
are going to examine a familiar group of animals of
in-between size-mammals, in particular mammals
that live on land. Remind the children that a mammal
is an animal with a backbone that produces milk to
feed its babies. Point out that a human being is a
mammal; then have them find the human being on the
Now have them find the shrew and the elephant on
the scale. Tell them that the shrew is the smallest
mammal that lives on land, and the elephant is the
largest. The mammals that they are going to learn
about now are in this shrew-to-elephant range (the
gray block on the scale). Explain that, to see how
these mammals change with size, they will begin by
comparing the smallest and the biggest. Then draw
on the "Shrews and Elephants" section of the background materials to give the children brief wordportraits of the two animals.
Next, explain to students that they are going to look
at why shrews and elephants differ in these ways. Tell
them that, to begin to understand why, they need to
know what metabolism is. Then draw on the "Metabolism" section of the background materials to explain what metabolism involves. Emphasize that metabolism is absolutely essential to animals because it
provides the energy and materials that they need to
survive and reproduce.
Point out that it is easy to see the effects of metabolism in action, since metabolic rate increases with
activity. To demonstrate, ask one of the children to
How much oxygen does its
whole body use each hour?
(in microliters* per hour)
How much oxygen does each
gram of its body use?
(in microliters per gram
per hour)
How fast does its heart beat
when it is resting?
(in beats per minute)
How long do its babies develop
inside the mother before they
are born? (in weeks)
*A microliter is a millIonth of a liter.
A cassowary, which weighs about 50 kilograms,
never takes to the air, because birds above 10
kilograms are too heavy to fly. (Jessie Cohen,
National Zoological Park)
Step 2: Size, Surface Area, and Heat
Have each child build a marshmallow representation
of an "animal" shaped like a cube that is 3 marshmallows long, 3 marshmallows wide, and 3 marshmallows deep, using toothpicks to hold the marshmallows together. Dr~w the shape on the chalkboard:
A very big adult giraffe can be almost twice as tall as
an elephant. But it is only about one-seventh as
heavy. (Jessie Cohen, National Zoological Park)
When the children have finished, ask them how
much their animal weighs, in marshmallow units (each
weighs 27 marshmallows). Write this on the chalkboard, under the drawing.
Now tell the children that, since animals are covered
with skin, they should paint their marshmallow animals to give them skin. (If they use diluted food coloring, they can safely eat their marshmallows later.)
While the marshmallows are drying, remind the children that the painted part, the skin, is called the surface
area of the animal. It is where the animal touches its
Have the kids take their animals apart, and imagine
that the 27 separate marshmallows are 27 little animals. Ask them how much all the little animals weigh
together, and write the answer on the chalkboard-to
emphasize that the weight of the 27 separate marshmallows is exactly the same as the weight of the 27
attached together. (Consider the toothpicks weightless.)
. Now ask whether the big animal has the same amount
Shrew-to-Elephant Table
How much does it weigh?
(in grams)
What is its lifespan?
(in years)
go to the front of the class and· do jumping jacks.
When the jumper is breathing hard, have the other
students count how many breaths the jumper takes in
a minute; have them compare that to the number of
breaths a nonjumper takes. Then ask them to make a
similar comparison for heartbeat rate (you may need
to show the children how to take a person's pulse).
Explain that the jumper's breath and heart rates have
gotten faster because his metabolism rate went up as
he became active. Metabolism requires oxygen; the
jumper needs to breathe faster to get more air. And
his faster-beating heart moves the blood around his
body more quickly, bringing more food and oxygen
to his cells, and carrying away the waste products of
metabolism sooner. Like the jumper, the shrew has a
fast breath and heart rate, and a high metabolic rate.
But unlike the jumper, the shrew has a very high
metabolic rate even when it is resting. Tell the children
that they are now going to use marshmallows to find
out why.
of skin as the group of 27 little animals together. The
children can see, by looking at their marshmallows,
that the little animals as a group have much more skin
than the single big animal did: the big animal had only
colored skin; the little animals have all the colored
skin plus a lot of white skin. This means that little
animals have more oftheir bodies touching the outside
world than big animals do.
Now carry the marshmallow analogy a little further
by telling the children to imagine for a moment that
every marshmallow produces heat, the same amount
of heat as every other marshmallow. Ask the children
to compare how much heat the 27 little animals produce together with how much heat the big animal
produces. The answer is, of course, that the total heat
produced is the same.
Then tell the children that when a warm animal's
body touches cooler air, it loses heat. Ask which will
lose more heat-the 27 little animals or the single
larger one? Of course, the 27 little animals will lose
more heat, because they have so much more surface
(skin) to lose heat through. Small animals lose more
heat than big animals do, because they have more
surface area.
Now use the "Body Temperature" section of the
background materials to explain to the children how
warm-blooded animals have physiological ways to keep
their body temperature constant, even when the temperature of their surroundings is changing.
Step 3: The Shrew-to-Elephant Table
Now your students are ready to use the Shrew-toElephant Table that appears on this page, in an activity
with two goals. The first goal is for the children to
extend what they have learned to the whole range of
land mammals that are between shrews and elephants
in size. The second goal is for them to practice laying
out numbers in a table and reading information off a
table-two very important skills.
Here is how the table can be used to do this.
First, read aloud, in random order, the names of
the mammals that appear as headings across the top
of the table. Ask the children to figure out how to
arrange the names in order of increasing size. Write
the children's answers across the top of the chalk-
• The question, "How much oxygen does its whole
body use each hour?" asks about the amount of oxygen
that the whole animal needs: bigger animals need more.
• The question, "How much oxygen does each
gram of its body use?" asks about the amount of
oxygen that each gram of the animal needs: bigger
animals "run on" less.
The rest of the table should be easy for the children
to understand. A good way to conclude Step 3 is by
telling the class about the other size-related patterns
described in "How Are Small Mammals Different
from Big Ones?"
After the children have finished these activities, give
them a chance to examine the poster (on the Pull-Out
Page) in as much detail as they want. You may wish
to spend some class time discussing the poster (the
sidebar, "Animal Sizes and Size Limits," provides
background information).
Then the kids are ready to have fun applying what
they have learned about animal size by writing and
illustrating a science fiction adventure based on real
facts. Here is the topic:
• You are a scientist who has invented a size potion
that can make you any size an animal can be. How
big or little you get depends on how much of the
potion you drink. Write a science fiction story describing the adventures you had two different times
you drank the potion. The first time, you became
bigger than you are in normal life; the second time,
you became smaller. You stayed each new size for
one hour.
Goliath beetles can be as long as 10 centimeters.
How long, would you guess, is this one at the Insect
Zoo in the National Museum of Natural History?
(Chip Clark, National Museum of Natural History)
board. (Throughout this activity, you are going to be
reproducing the table on the chalkboard; format everything you write on the board accordingly.)
Now write the first question, "How much does the
animal weigh?" in the appropriate place on the chalkboard. Then state each animal's weight as a sentence
("A shrew weighs 10 grams. "). After each statement,
fill in the animal's weight under its name, explaining
what you are doing.
Then write the other questions where they belong
on the table, and draw the lines of the grid. Tell the
children that you are now going to give them pieces
of information-out of order, and in sentence form.
They are to put each piece of information, as a number,
in the box where it belongs.
You will want to emphasize to the children that all
the answers on each line should be given in the same
measurement units. Point out how this is so in the
sample line. Explain that if the units were not the
same, it would be much harder to compare the different
animals. For example, ifthe small animals were measured in grams, and the big animals in kilograms, users
of the table would have to change all the answers into
grams (or all the answers into kilograms) before they
could glance at the table quickly and know which
animal was bigger than which. Remind the children
that this principle will apply when they make tables
in the future.
Now have each student reproduce the headings and
the grid on a piece of paper. Ask one child to go to
the chalkboard while the others continue to work in-
Step 4: Following-Up
You bet I'm big-for a frog! I'm an African bullfrog
and I weigh almost half a kilogram. (Jessie Cohen,
National Zoological Park)
gives you a picture of
sizes. Here are some
that the children may ask,
you may want to bring out, as you move up the
scale from the smallest to the largest animals.
(Any of these questions could be a research topic
for students who wish to look further into the
subject of animal size.)
• How small can an animal be? The bottom
limits of animal size are
Tell exactly what size you became in each case. Based
on what you have learned about how size shapes animals, describe at least four ways you changed as you
changed size. Tell about the adventures you had. Then
say which size you preferred being, and why you liked
life at that size better. Illustrate your story.
)ded animal. One
of small-sized anis that, generally speaking, the smaller an
animal is, the more young it produces.
• Why don't big animals col'lapse?
a person sits on a smnmY··1Cl!lle(!
breaks. In the same way,
animal would bend or break its
it. weren'l
for the fact that
animals haFe thicker bones
(and shells) compared 10 their size than small ones
animals also have thicker muscles.
, to move their heavier bodies.
. 'ker than the animal's
And the
dividtiiilly'8.t their seats. Giive one piece of information
at a time, for example, "A dog's heart beats 95 times
a minute" or" An elephant lives for about 60 years."
After each statement, give the children time to figure
out where the piece of information should go. Then,
as a check, have the student at the chalkboard write
the answer in the correct box.
After the table has been completed, you may want
to warn the children not to be surprised if they see
somewhat different answers in other tables or books.
There are tremendous variations among living creatures. No scientist can know for sure what the exact
average is for all animals, because no one can measure
every animal. Think, for example, of how many different sizes of dogs there are. No wonder that the
numbers you find in the "dog" column depend on
which kinds of dogs the person who figured out the
numbers was looking at.
Now it is time for the children to use the table they
have created. Have them go over it line by line. For
each line, ask them to describe the pattern that emerges
from the numbers in the line. For example, the heartbeat line shows that big animals have hearts that beat
less often than the hearts of the smaller animals. The
patterns that will emerge from the numbers in the table
are some of the ones described in "How Are Small
Mammals Different from Big Ones?" (in the background materials).
The pair of questions about oxygen consumption
(' 'How much oxygen does its whole body use in one
hour?" and "How much oxygen does each gram of
its body use in one hour?' ') are the only ones in the
table that may be confusing. The difference between
a value for the whole body of an animal and the value
for each gram of the animal's body weight has cropped
up repeatedly in this issue of ART TO ZOO. It came
up in connection with food consumption, for example,
when the children learned that an elephant ate a larger
total amount than a shrew, but that each gram of the
elephant's body used a smaller amount. Now is a good
chance to make sure that the class clearly understands
this important difference.
If the children had a pet elephant and a pet shrew,
they would have to spend a lot more money buying
the elephant's food than buying the shrew's. This is
what the whole body amount refers to. Yet each gram
of the elephant's body needs less food than does each
gram of the shrew's body. Tell the children that they
might think of the elephant as a huge but fuel-efficient
car, and of the shrew as a compact gas-guzzler. (This
analogy is very loose, but it may help the children
grasp the difference.)
The two questions on oxygen consumption in the
table reflect exactly the same distinction:
them to
still have plenty of surface area.
creatures (bacteria and one-celle
example) have so much surface area-and such
small total requircmcnts·,,·-that they can absorb all
the oxygen and nutrients they need right through
their outside surface.
Slightly larger animals could not get enough
oxygen and nutrients this way if they stayed so
simple in shape·-so their shapes tend to be more
complicated than those of their tiniest counterparts. The larger animals have folds, knobs, and
holes on the outside and inside surfaces of their
bodies. These make their surface area bigger, incr
for them.
Weight is less of a problem for animals that
live in water, because the water holds the anirnals
up. (Think of the damage a diver would inflict
on himself if he jumped off a high board into an
empty pool. Yet he can safely and happily jump
into a filled pool over and over again-~because
the water holds up his weight, slowing, and finally
stopping, his plunge.) For this reason, the blue
whale (the largest of all animals) can live quite
well in the ocean even though it is about] 4 times
as heavy as an elephant. Flowever, 11 beached
whale will die of suffocation under the weight of
its own body"
• What is the biggest animal possible? No
one really knows. Clearly an elephant is not the
largest land animal possible, since scientists know
that Baluchitherium. a prehistoric relative of the
rhinoceros, definitely lived on land even though
it weighed as much as four elephants.
• What about dinosaurs? Brachiosaurus was
the biggest dinosaur that ever lived. weighing
about as much as 14 ele hants. Scientists used to
big beow
back over your shoulder
ant running down the street after you-relax, you must be asleep and dreaming!
continued ./hnn page /
heat). And they can stay active even in cold weather.
But heating itself costs a warm-blooded animal a
lot of energy. To fuel its more intense metabolic processes, it has to eat considerably more than does a
cold-blooded animal. To minimize these energy costs,
it may also reduce its heat loss by other means-by
migrating to a warmer climate, by hibernating, by
insulating itself with fur or fat, by building an insulated
nest, or by huddling with others of its kind. But if
these means are not enough to keep the animal warm,
it shivers, increasing its activity level and raising its
metabolic rate.
Because not all animals lose (or gain) heat at the
same rate, not all animals are affected equally by being
in cold (or hot) surroundings. Small animals lose and
gain heat more easily than do big animals.
One reason for this is that heat transfer between an
animal and its surroundings takes place at the surface
of the animal's body, and a small animal has more
surface, compared to its size, then does a large animal
of the same shape. (This is a simple fact of geometry,
true of any object, whether living or nonliving: when
the volume of the object triples, its surface area only
Dr. Steve Thompson, a zoologist at the National
Zoological Park in Washington, D.C., has just
determined the metabolic rate of this tenrec by
measuring how much oxygen it uses. (Aaron
The fact that small animals lose heat more easily
than do large animals accounts for** many of the
differences between the shrew and the elephant-and
between small and large mammals in general. The
shrew, being very tiny, has a relatively large surface
area; consequently, it loses a lot of heat. By maintaining a high metabolic rate, it also produces a lot
of heat, so it is able to keep its internal body temperature constant despite its high rate of heat loss.
How Are Small Mammals Different from Big
The shrew is the most extreme case, but it is generally
true that the smaller the mammal, the higher its metabolic rate. And when we consider what metabolism
involves, it is no surprise that a number of different
body processes related to metabolism also change with
size. Here are some of them:
• A small mammal has a higher oxygen turnover.
Every hour, a resting mouse needs about 2,000 microliters of oxygen per gram of body weight; a man,
about 200 microliters; and an elephant, only about 100
**At one time, scientists thought that the surface area explanation
given here could in itself fully explain why small animals have
higher metabolic rates. However, as they studied more animals,
they found that, although surface area and metabolism increase
together, they increase at somewhat different rates-so surface area
is not a full explanation. Nevertheless, it is a clear and pedagogically
fruitful one, and surface area is an important constraint on the
metabolic rate that a warm-blooded animal can have.
Smithsonian National Seminar for Teachers
You don't have to live in Washington to study at the
"Teaching Writing Using Museums and Other
Community Resources," a special one-week course,
will be offered by the Smithsonian Institution this
summer for elementary and secondary teachers living
more than 75 miles outside the Washington, D.C.,
metropolitan area.
The course carries graduate credit from the University of Virginia. Tuition and materials fees will
total approximately $275. No scholarships are available.
"Teaching Writing Using Museums" will survey
ways in which teachers can use local museum exhibits
and such diverse resources as cemeteries and houses
as tools for teaching writing. In addition to working
on formal and informal exercises, participants will
interview several Smithsonian staff writers to learn
about various approaches to writing.
The course, worth three graduate credits, is open
to full-time classroom teachers (grades 5 through 12),
school librarians (media specialists), and curriculum
specialists. Interpreters for hearing-impaired individuals can be provided for all class work.
Classes will meet from July 7 to 16 in Washington,
D.C. Specially priced housing may be available in a
conveniently located college dormitory. Participants
will arrange their own meals.
Enrollment is limited. Applications must be postmarked no later than April 13. Notices of acceptance
will be mailed by May 4.
For an application form, including complete information, write:
National Seminars
Office of Elementary and Secondary Education
Arts and Industries Building, Room 1163
Smithsonian Institution
Washington, D.C. 20560
Or, telephone (voice) 202/357-3049 or (Telecommunications Device for the Deaf) 202/357-1696.
• A small mammal breathes faster. While a mouse
may take 150 breaths a minute, a man takes about 16,
and an elephant only 6.
• The heart of a small mammal beats faster.
• The blood of a small mammal circulates through
its body faster. A shrew's blood circulates all the way
around in 4 seconds, a horse's in 90 seconds, and an
elephant's in 140 seconds. This, and the fast heartbeat,
make sense when you consider that the blood must
carry food and oxygen to the cells for use in metabolism, and must carry away the waste products that
metabolism creates.
• A small mammal eats more per gram of its body
weight. In other words, the total amount of food that
it eats is less, but it provides more food for each of
its cells.
• A small mammal develops inside its mother for
a shorter time before it is born. A mouse has a gestation time of about 3 weeks; a horse, of 11 months;
and an elephant, of about 22 months.
• A small mammal has babies when it is younger.
The length of a generation can range from 2 months
for a shrew, to almost 15 years for an elephant.
• A small mammal has a shorter lifespan.
What is even more surprising than these differences
is that the total number ofbreaths and the total number
of heartbeats in a lifetime are approximately the same
for most mammals (330 million breaths, and 11/2 billion heartbeats). Just as an inheritance that lasts a miser
a lifetime passes through a spendthrift's hands in a
year, so an elephant manages to make its allotted
number of breaths and heartbeats last six decades,
while a shrew has consumed them all in 12 months.
Scientists do not know why this is so. Maybe one
of your students will figure out why, sometime in the
future. There are exceptions to these patterns. Human
beings, in fact, are an exception to the pattern. According to our size, we should have a lifespan of less
than 30 years.
Cloudsley-Thompson, J.L. The Size of Animals.
Meadowfield Press, Durham, England, 1977.
Smithsonian institution Press
Associate B'diwr: Michelle K, Smith
Dc,\'iwu:r:, Joan Wolbier
McMahon, Thomas A., and John Tyler Bonner. On
Size and Life. Scientific American Library, New
York, 1983.
Schmidt-Nielson, Knut. "Scaling in Biology: The
Consequences of Size, " Journal of Experimental
Zoology 194, 1975.
Wells, H.G., J.S. Huxley, and G.P. Wells. The Science ofLife. Pages 936-44. Doubleday, Doran and
Company, Garden City, New York, 1938.
This issue of ART TO ZOO is particularly indebted
to the teaching suggestions in "You and a Shrew,"
in Ranger Rick's NatureScope, Amazing Mammals,
Part II (pages 56-58), published by the National Wildlife Federation, Washington, D.C., 1986.
Books for Children
Crump, Donald J., editor. Giants from the Past. National Georgraphic Society, Washington, D.C., 1983.
Ford, Barbara. Why Does a Turtle Live Longer than
aDog? William Morrow and Company, New York,
Grigson, Geoffrey, and Jane Grigson. Shapes, Animals and Special Creatures. Vanguard Press, New
York, 1985.
Lavine, Sigmund A., and Vincent Scuro. Wonders of
Elephants. Dodd, Mead and Company, New York,
Patent, Dorothy Hinshaw. Sizes and Shapes in Nature-What They Mean. Holiday House, New York,
Books for Teachers
Rahn, Joan E. Keeping Warm, Keeping Cool .. Atheneum, New York, 1983.
Calder, William A., III. Size, Function and Life History. Harvard University Press, Cambridge, Massachusetts, 1984.
Tison, Annette. Big Book ofAnimal Records. Putnam
Publishing Group, New York, 1985.
Special thanks to the foil
for their help in prep ,
Smithsonian staff members
sue of ART TO Zoo:
National Museum of Natural History: Robert Hoffman, Di·
rector; Joan Madden. Chief. Office of Education,
Editor: Bctsy Eisendrath
Hiley, Peter. "How the Elephant Keeps Its Cool,"
Natural History, December 1975.
Peters, David. Giants of Land, Sea and Air. Knopf,
New York, 1986.
Haldane, J.B.S. "On Being the Right Size." In: Possible Worlds. Harper, New York, 1928.
is a publication of the
Office of Elementary and Secondary Education
Smithsonian Institution. Washington. D.C. 20560
During a class exercise,
a National Seminar
participant writes about
an airplane exhibited in
the Smithsonian's
National Air and Space
Our reason j~)r
moting the use ql
teachers na,'i01U1/l
all of us here at
Working as we do with a v
that literally contain the
we believe that objects (be they works of art. natural history
specimens, historical artifacts. or live animals) have a tre,
mendoLls power to educate. We maintain that it is equally
important for students to learn to use objects as research
tools as it is for them to learn to use words and numbersc~.,
and you can find ohjects close at hand. by
on the
resources of your own community,
Our idea. then. in producing ART TO ZOO is (0 sharc with
VOl'I«,..,-,aml you with us··....methods of
with students
that Smithsonian staff members have found suc·
National Zoological Park: Steve Thompson. Research Associate.
Office of Elerllt~ntary and Secondary Education: Ann Bay.
Thomas Lowderbaugh. Janice Majewski. and Barbara
We arc also
to the following individuals for their
help in tracking down pictures:
National Museum of Natural
Frank Greenwell.
Charles O. Handley, JL,
Love. John Miles, Sheila
Stoller. and Barbara Van Creveld,
National Z()<ological Park: Jessie Cohen. Edwin Gould, William Xanteu,
...._~ ..,.,..~._.,.'_ .. _.~.~.~~~--~---------------------------------------------------------------------,
Animal Sizes and Size Li its
To get an idea ofthe size range that this scale covers: the blue whale is 1 ,000,000,000,000,000,000,000,
(one sextillion) times bigger than Mycoplasma. If an animal existed that was that many times bigger
than the blue whale, this imaginary animal would have 100 times the volume of the earth.
The upper limits of size are mostly
physical ones resulting from gravity.
Bigger animals weigh more. Their
bones have to hold up this greater
weight, and their muscles have to
move it around. There comes a size
where they can no longer do this.
Animals that live in water can
be much heavier than animals that
live on land, because the water helps
hold up their weight. This is why
a whale can be so much larger than
an elephant-and than all the dinosaurs-as long as it stays in the
water. A blue whale washed onto
a beach will die of suffocation, because the weight of its own body
will keep it from breathing.
This is one reason that giants
could not exist-unless thyy lived
underwater, or on a planet where
gravity was much weaker than it is
on earth.
blue whale (100 tons)Largest animal alive and
largest that has ever existed.
Brachiosaurus (80 tons)Largest dinosaur. People
used to think it lived mostly
in water, but now think it
may have spent a lot of its
time on land.
Baluchitherium (30 tons)Largest land mammal of all
Animals this big have
lungs or gills that increase the surface area
through which they
absorb oxygen. They
also have blood that·
. carries oxygen around
their body.
The largest animals. Do you see the human
being (who looks as if he were standing
inside the blue whale)? Look at the picture
of the elephant in this issue of ART TO Zoo,
and try to figure out how big it would be if
it was in this box. Cut out a paper elephant
and try it here for size!
1, the largest flying bird (albatross); 2, the largest
known animal (blue whale); 3, the largest extinct land
mammal (Baluchitherium) with a human figure shown
for scale; 4, the tallest living land animal (giraffe);
5, the dinosaur Tyrannosaurus; 6, another dinosaur,
Diplodocus; 7, one of the largest flying reptiles (Pteranodon); 8, the largest extinct snake; 9, the length
of the largest tapeworm found in man; 10, one of the
largest living repitles (American crocodile); 11, the
largest extinct lizard; 12, the largest extinct bird; 13,
the largest jellyfish; 14, the largest living lizard (Komodo dragon); 15, sheep; 16, the largest bivalve mollusk; 17, the largest fish (whale shark); 18, horse;
19, the largest crustacean (Japanese spider crab); 20,
the largest extinct sea scorpion; 21, large tarpon; 22,
the largest lobster; 23, the largest mollusk (deep-water
squid); 24, ostrich; 25, the lower 32 meters of the
largest organism (giant sequoia tree), with a 30-meter
larch tree drawn in front of it
Medium-sized animals. The adult human hand (18) gives
you a scale of comparison.
ant (under 1 gram)-An
average ant colony, with
over a million ants, together
weighs less than a heavy
flea (0.3 milligrams)-If
you ordered a kilogram of
fleas, your package would
contain 3 million of them.
Insects this big pump
air through holes in
their skin into air tubes
in their body. From
the air tubes, the air
spreads through the
animal by diffusion.
large amoeba (0.1
1, dog; 2, herring; 3, the largest egg; 4, song thrush with egg; 5, the
smallest bird (hummingbird) with egg; 6, queen bee; 7, common cockroach; 8, the largest stick insect; 9, the largest polyp; 10, the smallest
mammal (shrew); 11, the smallest vertebrate (a tropical frog); 12, the
largest frog (goliath frog); 13, common grass frog; 14, house mouse; 15,
the largest land snail (Achatina) with egg; 16, common snail; 17, the
largest beetle (goliath beetle); 18, adult human hand; 19, the largest
starfish; 20, the largest free-moving protozoan (an extinct nummulite)
Animals that are small, but big enough to see with your naked
eye. The frog (5) is the same one that is the smallest creature in
the second box.
1, one of the smallest fishes; 2, common brown hydra, expanded; 3, housefly;
4, medium-sized ant; 5, the smallest vertebrate (a tropical frog); 6, flea; 7, the
smallest land snail; 8, common water flea (Daphnia)
rotifer (considerably under
0.0001 milligrams)Smallest many-celled animal
average bacterium
(0.0000000001 milligrams)
The lower limit of size is set by
biochemistry. You have learned that
animals need to metabolize to stay
alive-so they have to be at least
large enough to hold the metabolic
and genetic equipment they need.
Animals this big can
absorb the oxygen they
need through the surface of their body.
Mycoplasma (under
milligrams)-Smallestsinglecelled organism.
Winter 1987
News for Schools from the Smithsonian Institution
Some ofthe largest microscopic animals and cells, and the smallest creatures that you can see with your naked eye. Note the flea's
front leg (11). The whole flea appears in the third box.
1, Vorticella, a ciliate; 2, the largest ciliate protozoan (Bursaria); 3, the smallest
many-celled animal (a rotifer); 4, smallest flying insect (Elaphis); 5, another
ciliate (Paramecium); 6, cheese mite; 7, human sperm; 8, human ovum; 9,
dysentery amoeba; 10, human liver cell; 11, the front leg of a flea
All drawings are from On Size and Life by Thomas A. McMahon and John Tyler Bonner.
Copyright © 1983. Reprinted with the permission of Scientific American Library.
am nos de Animales y Limites de Tamano
Para hacerse una idea de las proporciones que abarca esta escala, la ballena azul es 1,000,000,000,000,000,000,000
veces mas grande que la Mycoplasma. Si existiera un animal que fuera tantas veces mas grande que la ballena azul,
ese animal imaginario tendria 100 veces el volumen de la Tierra.
El tamafio de los animales
gigantescos es limitado par la fuerza
de gravedad.
Los animales mas grandes pesan mas.
Sus huesos tienen que ser capaces de
sostenerlo, y sus musculos capaces de
mobilizarlo. Esto ya no es posible
cuando un animal alcanza cierto
Los animales que viven en el agua
pueden ser mucho mas pesados que
los que viven en la tierra, porque el
agua les ayuda a sostener su peso. Es
par eso que una ballena puede ser en
tal medida mas grande que un
elefante-y mas grande que todos los
dinosaurios-mientras permanezca en
el agua. Una ballena azul arrastrada
por las olas hacia la playa morirfa de
asfixia porque su propio peso no la
dejarfa respirar.
Esta es una de las razones por las
cuales no pueden existir los gigantes ,
a menos que vivieran bajo el agua 0
en un planeta don de la fuerza de
gravedad sea mucho menor que en la
BaHena azul (l00
toneladas)-EI animal mas
grande en existencia, tanto
en el pasado como
Brachiosaurus (80
toneladas)-El dinosaurio
mas grande. Antes se crefa
que vivfa basicamente en el
agua, pero ahara se cree que
puede haber pasado gran
parte del dfa en la tieIJa.
Los animales mas grandes. l, Ve usted al ser
humano que se ve como si estuviera parado
dentro de la ballena azul? Mire la figura del
elefante en este ejemplar de ART TO Zoo,
y trate de imaginar cuan grand~ serfa si estuviera en este cuadro. Recorte un elefante
de papel y trate de ver como cuadra en este
Baluchitherium (30
toneladas)-EI mamffero
terrestre mas grande de
todos los tiempos.
. ==========
Animales de este tamafio tienen pulmones 0 agallas que
aumentan el area de
superficie a traves del
cual ellos absorben
oxfgeno. Tambien
tienen sangre que
transporta el oxfgeno
a traves de su cuerpo.
1,EI ave voladora mas grande (albatr6s); 2, el animal
mas grande que se conoce (ballena azul); 3, el mamffero terrestre extinto mas grande (Baluchitherium) con
una figura humana presentada como referencia de
escala; 4, el animal terrestre viviente mas alto (jirafa);
3, el dinosaurio Tyrannosaurus; 6, otro dinosaurio,
Diplodocus; 7, uno de los reptiles voladores mas grandes
(Pteranodon); 8, la culebra mas grande extinta; 9, la
longitud de la lombriz solitaria mas grande que se ha
encontrado en un hombre; 10, uno de los reptiles
vivientes mas grandes (cocodril0 americano); 11, el
mas grande de los lagartos extintos; 12, el ave extinta
mas grande; 13, la medusa mas grande; 14, el lagarto
mas grande viviente (drag6n de Komodo); 15, oveja;
16, el molusco bivalve mas grande; 17, el pez mas
grande (tibur6n baIIena); 18, caballo; 19, el crustaceo
mas grande (cangrejo arafiajapones); 20, el escorpi6n
marino extinto mas grande; 21, tarp6n grande; 22, la
langosta mas grande; 23, el molusco mas grande (calamar de aguas profundas); 24, avestruz; 25, los 32
metros inferiores del organismo mas grande (arbol
sequoia gigante) con un alerce (larice) de 30 metros
dibujado en frente.
Algunos animales de tamafio mediano. La mana de un adulto
les da una comparaci6n.
I, Perro; 2, arenque; 3, el huevo mas grande; 4, tordo (zorzal), con
huevo; 5, el pajaro mas pequeno (picaflor) con huevo; 6, abeja reina; 7,
cucaracha comiln; 8, el mas grande los insectos-palo; 9, el p6lipo mas
grande; 10, el mamffero mas pequeno (musarana); II, el vertebrado mas
pequeno (una rana tropical); 12, la rana mas grande (rana goliat); 13,
rana de pasta comiln; 14, un rat6n casero; 15, el caracol terrestre mas
grande (Achatina) con huevo; 16, caracol comiln; 17, el escarabajo mas
grande (escarabajo goliat); 18, mana humana adulta; 19, la estrella de
mar mas grande; 20, el protozoo m6vil mas grande (un nummulite extinto).
La hormiga (menos de 1
gramo)-Una colonia
promedio-de mas de un
mill6n de hormigas-pesa
menos que un hombre
La pulga (0.3
miligramos)-Si Ud.
quisiera comprar un kilo de
pulgas, el paquete contendrfa
3 millones de ellas.
Los insectos de este
tamafio bombean el
aire a traves de agujeros en su piel hacia
tubos respiratorios en
su cuerpo. De estos
tubos el aire se extiende a traves de todo
el cuerpo del animal
por difusi6n.
La ameba grande (0.1
Algunos animales que son pequefios pero 10 suficientemente grandes
como para poder ser observados a simple vista. La rana (5) es
la misma que aparece como la criatura mas pequefia en el
segundo recuadro.
I, Uno de los peces mas pequenos; 2, hidra comiln, ampliada; 3, mosca domestica; 4, hormiga de tamano promedio; 5, el vertebrado mas pequeno (una
rana tropical); 6, pulga; 7, el caracol terrestre mas pequeno; 8, pulga comiln
de agua (Daphnia).
EI rotifero
(considerablemente menos
de 0.0001 miligramos)-El
animal multicelular mas
Una bacteria de tamaiio
promedio-(O.000000000 1
miligramos) .
La bioqufmica determina el lfmite
inferior en cuanto al tamaiio. Dds. saben·,
que los animales tienen que metabolizar
para mantenerse vivos. Asf es que deben
tener el tamafio mfnimo como para
poder contener el aparato metab61ico
y genetico que necesitan.
Mycoplasma (menos de
unicelular mas pequeno.
Los animales de este
tamafio puede absorber el oxfgeno que
necesitan a traves de
la superficie de su
Vista de algunas celulas y animales miCroscoPlCOS de mayor
tamafio y algunas de las criaturas mas pequefias que se pueden
ver a simple vista. Ffjense en la pata delantera de la pulga (11).
La pulga entera aparece en el tercer recuadro.
I, Vorticella, una ciliada; 2, el protozoo ciliado mas grande (Bursaria); 3, el
animal multicelular mas pequeno (un rotffero); 4, el insecto volador mas pequeno
(Elaphis); 5, otro ciliado (Paramecium); 6, acaro; 7, esperrnatozoide humano;
8, ovulo humano; 9, ameba de la disenterfa; 10, celula del hfgado humano; 11,
pata delantera de una pulga.
Traducido por el Centro Hispano de Desarrollo Educativo (SED Center)
Todos las dibujos de los animales son de On Size and Life par Thomas A. McMahon y
John Tyler Bonner. Derechos reservados 1983. Reimpresi6n con permiso de Scientific
American Library.